1. Field of the Invention
The invention relates to a bearing shell with at least one retaining cam, which comprises an outer contour which is rectangular when the partial surface of the bearing shell is viewed from above and an indentation on the inside of the bearing shell. The invention also relates to a method of producing cams in bearing shells by pressing outwards into a rectangular die a small portion of the bearing shell wall in the area of the partial surface.
2. Description of Related Art
Retaining cams on bearings shells have the task of easing installation of the bearing shell, by defining the installation position in the bearing housing in cooperation with a recess provided therein. When the partial surface 2 of the bearing shell 1 is viewed from above, such retaining cams 3, known for example from DE-AS 1477052, comprise, as shown in FIG. 1, a rectangular outer contour and a rectangular inner contour. The retaining cam 3 is provided so as to position itself in the milled-out portion 5 on insertion into the bore in the bearing housing 4. In the region of the retaining cam 3, the partial surface 2 then lies in the plane of the partial surface 6 of the bearing housing and then rests against the closed parting plane of the second housing half. This not only results in fixing of the installation position but also in the prevention of rotation of the bearing shell within the housing bore during operation.
The retaining cams 3 may be beaten by means of a blade or, as described in DE-AS 1477052, produced in the gap in a roll pair. However, a disadvantage of all known retaining cams is the small transition area 7a,b between the cam 3 and the adjacent bearing wall. The transition area should be understood to mean the area between the base 8a,b of the cam and the indentation 9. In general, the material of the bearing shell is torn or even sheared off in this area, such that material detachment may occur there during operation. To prevent this, in many instances the inside of the bearing shell is adjusted by milling in the area of the indentation 9. In the case of heavily loaded bearings, the cam may possibly tear away under the action of the forces and vibrations arising during operation owing to the only slight connection with the rest of the bearing shell in the upper area.
It has therefore already been proposed to provide pin-shaped elevations in the bearing housing, which engage in corresponding bores in the bearing shell. This is described, for example, in the Clevite brochure "Mechanics Engine Bearing Reference Manual, First Edition, 1954". This solution is only possible, however, with bearing housings which have a suitably thick wall.
U.S. Pat. No. 2,124,060 discloses a retaining cam with round inner and outer contour, which projects only slightly outwards, however, such that it cannot adequately fulfill its function as a rotation prevention device. In the production of round cams which do project sufficiently far outwards, it has been found that the nominal width, which is predetermined by the milled-out portion in the bearing housing, cannot be maintained because of gentle transition areas. It is thus impossible to locate the bearing shell cleanly against the housing and position and fix it with axial precision.
These disadvantages may be prevented if the cam is produced only in the area of the bearing backing, in order thereby not to damage the running surface. DE 3230700 C2 discloses so-called upset cams, wherein, by the exertion of pressure directed perpendicularly at a radially outer, axially defined area of the partial surface and with appropriate bracing at the bearing inner surface, material is displaced radially outwards. Between the indentation arising through material displacement and the inner surface there remains a supporting strip of material. This method may, however, only be used with thick bearing shells with wall thicknesses &gt;2 mm.
Since developments in engine construction are moving in the direction of thinner walled, i.e. lighter, bearing housings and also of thinner bearing shells, which additionally are exposed to ever higher loads, for instance speeds of up to 17000 rpm in racing, alternatives to the known solutions are being sought.